Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing. Ink jet printing mechanisms can be categorized by technology, as either drop on demand ink jet or continuous ink jet.
The first technology, drop-on-demand ink jet printing, typically provides ink droplets for impact upon a recording surface using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of an ink droplet that crosses the space between the printhead and the print media and strikes the print media. The formation of printed images is achieved by controlling the individual formation of ink droplets, as is required to create the desired image. With thermal actuators, a heater, located at a convenient location, heats the ink causing a quantity of ink to phase change into a gaseous steam bubble. This increases the internal ink pressure sufficiently for an ink droplet to be expelled. The bubble then collapses as the heating element cools, and the resulting vacuum draws fluid from a reservoir to replace ink that was ejected from the nozzle.
The second technology, commonly referred to as “continuous stream” or “continuous” ink jet printing, uses a pressurized ink source that produces a continuous stream of ink droplets. Conventional continuous ink jet printers utilize electrostatic charging devices that are placed close to the point where a filament of ink breaks into individual ink droplets. The ink droplets are electrically charged and then directed to an appropriate location by deflection electrodes. When no print is desired, the ink droplets are directed into an ink-capturing mechanism (often referred to as catcher, interceptor, or gutter). When print is desired, the ink droplets are directed to strike a print medium.
A number of different nozzle arrangements are used with various types of printers described above. While, FIGS. 1a-1d show representative nozzle architectures for drop-on-demand printhead, the thermal and piezoelectric actuators described below, can also be found in nozzle architectures for continuous printheads.
FIG. 1a shows, in cross-sectional side view, the basic arrangement of an ejector 10 for one type of drop-on-demand ink jet printer, commonly termed a “roof-shooter device,” and disclosed, for example, in U.S. Pat. No. 6,582,060 issued to Kitakami, et al. on Jun. 24, 2003. A bubble-jet heater provides a drop-forming mechanism 12 for ejecting ink from a nozzle orifice 14 of a fluid chamber 16 formed on a body 38 from a polymer material. The vapor bubble expands in the same direction as the direction of the ejected drop. With this arrangement, nozzle orifice 14 is part of a structure that is permanently bonded to a substrate 18 in the location of arrows 17.
FIG. 1b shows a schematic cross-sectional side view of an alternate ejector 10 arrangement in a drop-on-demand ink jet printer utilizing a thermal microactuator device, such as that disclosed in U.S. Pat. No. 6,631,979, issued to Lebens et al. on Oct. 14, 2003, and U.S. Pat. No. 6,598,960 issued to Cabal et al. on Jul. 29, 2003, as drop-forming mechanism 12 for ejecting ink from a nozzle orifice 14 of an fluid chamber 16. As with the FIG. 1a configuration, nozzle orifice 14 is permanently fixed in size and position as part of a structure bonded to substrate 18 in the location of arrows 17.
FIG. 1c shows a cross-sectional side view of another alternate ejector 10 arrangement in a drop-on-demand ink jet printer utilizing a piezoelectric actuator as drop-forming mechanism 12, and disclosed, for example, in U.S. Pat. No. 6,609,778 issued to Ingham, et al. on Aug. 26, 2003. Here, nozzle orifice 14 is provided by a nozzle plate 19 that is permanently bonded to fluid chamber 16 in the location of arrows 17.
FIG. 1d shows a cross-sectional side view of ejector 10 components in another type of drop-on-demand printer, commonly termed a “back-shooter device” type, and disclosed, for example, in U.S. Pat. No. 6,561,626, issued to Min et al. on May 13, 2003, using a thermal bubble-jet heater as drop-forming mechanism 12. The vapor bubble expands in a direction opposite the direction of the ejected drop. With this arrangement, nozzle plate 19, permanently bonded to substrate 18, forms part of the enclosing structure for fluid chamber 16 along with body 38 in the location of arrows 17.
In conventional continuous and drop-on-demand printhead design, nozzle plates are permanently bonded to the body of the printhead using various manufacturing techniques. For example, U.S. Pat. No. 6,644,789, issued to Toews, III on Nov. 11, 2003 discloses an arrangement using a photoresist layer having nozzle apertures laminated to another photoresist layer on the body of the printhead. U.S. Pat. No. 5,900,892 issued to Mantell et al. on May 4, 1999 discloses a nozzle plate fabricated using a photolithographic process, permanently bonded to the body of a printhead.
Additionally, and referring back to FIGS. 1a-1d, printheads are conventionally fabricated with a fixed diameter for nozzle orifice 14. The dimensions of nozzle orifice 14 are tailored to the viscosity and related drop-forming characteristics of a particular ink. While this arrangement may be expedient for many types of applications, this relatively inflexible dimensional constraint has some drawbacks. For example, by using a fixed diameter for nozzle orifice 14, a printing apparatus can be constrained to using only a narrow range of inks having a narrow range of viscosity or surface tension. Fixed nozzle orifice 14 dimensions also constrain possible droplet volumes to within a narrow range. Additionally, while it would be desirable to be able to vary the nozzle size of a given printhead instead of constructing a new printhead, no such technology has been commercialized.
Another disadvantage of conventional ejector 10 designs relates to cleaning. Numerous types of devices are employed for cleaning ink jet nozzles 10, both automatically and by hand. Using permanently bonded structures for nozzles 10 complicates the task of cleaning and refurbishing an ink jet printhead. A clogged nozzle plate, if bonded to the printhead using permanent adhesives such as epoxies, may render it economically impractical to clean the printhead, necessitating replacement of the complete printhead as a unit.
Thus, it can be appreciated that a more flexible ink jet nozzle plate design could provide substantial benefits for ease of use, equipment maintenance, and overall versatility of a printing apparatus.